Thousands of Australians may have high blood pressure but not know it, despite having the tests. The results of a new study have identified the condition of "masked hypertension" - when high blood pressure isn't identified in clinical tests - in approximately one in five participants. "These results clearly suggest we need to make changes in screening and treatment plans as soon as possible," Baker Heart and Diabetes Institute specialist Geoff Head said on Thursday. High blood pressure is a major factor for heart attack and stroke, he added. "Although the common assessment of hypertension has been via clinic measurements, this technique has limitations," Professor Head said. The test could help people like Rick Talbot, who has a family history of heart problems. Mr Talbot's grandfather died aged 59 and his father at 64 from a heart attack. His brother had a heart attack at 50. He himself was diagnosed with five blocked arteries and had a triple bypass but three years later he had a mini stroke. Researchers say for people like Mr Talbot, getting the right blood pressure diagnoses is crucial as blood pressure is linked to death from heart attacks and stroke. It was important that 24-hour blood pressure testing should be subsidised under Medicare to help identify the condition. "First we have to encourage GPs to diagnose high blood pressure using the most appropriate methods and ... (then) make screening cheaper for those who cannot afford it," Prof Head said. The results of the study have been published in the Journal of Hypertension with more than 4000 participants involved. Australian Associated Press